With the development of technology and the explosive growth of data services, more and more low-power base stations such as pico cells and home NodeB stations are deployed to provide small local coverage. This type of base stations may be collectively called as small cells. In wireless communications, the base station uses one single antenna or multiple antennas to achieve wireless signal coverage of a particular area which is also called the cell. The term cell is also usually used to refer to a logical entity that includes base station software and hardware sub-systems that serve user terminals within this particular coverage area. The deploying of small cells not only extends the coverage of macro cells, but also improves the throughputs of the particular area. Generally, the more small cells are deployed in the network, the more users can be served by the small cells and enjoy the performance gains brought by the small cells, so that the overall network throughput is greatly improved. It can be expected that in a real network, a large number of small cells are likely to be densely deployed in geographic areas where service requirements are concentrated.
In the actual deployment scenario of small cells, numerous cells may use separate cell identifications (IDs), or numerous adjacent small cells and/or transmission points (TPs) (hereinafter referred to as small cell/TP) share the same cell ID. Since the number of user equipments (UEs) served by one single small cell/TP is small, the service load of the single small cell/TP fluctuates a lot during different time periods. In order to save energy and reduce the interference to other small cells/TPs, the small cell on/off technology may be used to turn on or off the small cell/TP based on the actual service situation when small cell/TP has no service to be transmitted. The small cell/TP is required to periodically transmit the discovery signal in order for the UE to discover the turned-off small cell/TP so that the small cell/TP that has been turned off may be turned on when the UE has services to be transmitted.
Currently, cellular communication networks use licensed spectrum resources to carry out network deployment and service transmission. That is, the small cells/TPs periodically transmit the discovery signal in the licensed spectrum resources. However, with the increase in the number of base stations and the growing shortage of spectrum resources, there may be no spectral resources to be allocated for the discovery signal or strong interference caused by sending the discovery signal.